1. Field of the Invention
The present invention relates to charged particle beam equipment that scans a sample with a charged particle beam to form an image based on signals produced by the sample by the charged particle beam irradiation. Particularly, the invention relates to charged particle beam equipment capable of correcting magnification errors.
2. Background Art
Examples of equipment for observing a magnified image of a sample using a charged particle beam include the scanning electron microscope, the scanning transmission electron microscope, and the focused ion beam (FIB) system. In such charged particle beam equipment, observation magnification is defined by the ratio of the amount of scan of the sample surface with the charged particle beam to a magnified image based on the detection of secondary electrons or the like obtained from the scanned area. The amount of scan of the sample surface with the charged particle beam can be changed as desired through the magnitude of an electric or magnetic field that is caused to act on the charged particle beam by a scan mechanism. For example, in the case of a scanning electron microscope that employs electrons as a charged particle and which uses magnetic fields as an electromagnetic lens and an electron scanning mechanism, the magnification of a secondary electron image of the sample can be changed by changing the magnitude of the current applied to the electron beam scanning coil so as to change the area of the sample scanned with the electron beam. By reducing the electron-beam-scanned area on the sample, the magnification of the secondary electron image increases; by increasing the area, the magnification decreases.
In conventional charged particle beam equipment, such as the scanning electron microscope or the focused ion beam system, in order to measure the amount of scan by the charged particle beam, i.e., the magnification of a sample magnified image, accurately, the spacing size that indicates size characteristics is measured using a scanning secondary electron image or a scanning transmission electron image of a microscale sample having a known size or a crystal lattice. Any discrepancy between the reference size value and a measured value is given as a discrepancy in magnification, or a magnification error. Methods for such size measurement include a method by which a cursor is aligned with two points to be measured on an electron image to measure the size between the two points, and a method by which the size is measured through frequency analysis of an electron image by a Fourier transform (FFT). Patent Document 1, for example, discloses a technique for measuring the size through frequency analysis of an electron image by a Fourier transform (FFT).
Patent Document 1: JP Patent Publication (Kokai) No. 2005-209488 A